AP Chemistry
8.11 pH and Solubility
8.3 Weak Acid and Base Equilibria
A student investigates the effect of \(\text{pH}\) on the solubility of three hypothetical sparingly soluble salts: \(\text{MX}\), \(\text{MY}\), and \(\text{MZ}\). Each salt has a \(1:1\) cation-to-anion ratio and dissolves according to the generic equation:
\[ \text{MA(s)} \rightleftharpoons \text{M}^+\text{(aq)} + \text{A}^-\text{(aq)} \]
The student gathers the equilibrium data shown in the table below at \(298\text{ K}\).
Equal volumes of saturated solutions of each salt (each in contact with excess solid) are treated with a strong acid to lower the \(\text{pH}\) from \(7.0\) to \(2.0\). Which of the following correctly ranks the salts from greatest to least increase in molar solubility upon acidification, and provides the correct justification?
\[ \text{MA(s)} \rightleftharpoons \text{M}^+\text{(aq)} + \text{A}^-\text{(aq)} \]
The student gathers the equilibrium data shown in the table below at \(298\text{ K}\).
| Salt | \(K_{sp}\) at \(298\text{ K}\) | Anion | \(pK_b\) of Anion at \(298\text{ K}\) |
|---|---|---|---|
| \(\text{MX}\) | \(1.0 \times 10^{-10}\) | \(\text{X}^-\) | \(4.2\) |
| \(\text{MY}\) | \(1.0 \times 10^{-8}\) | \(\text{Y}^-\) | \(9.5\) |
| \(\text{MZ}\) | \(1.0 \times 10^{-6}\) | \(\text{Z}^-\) | \(16.2\) |
Equal volumes of saturated solutions of each salt (each in contact with excess solid) are treated with a strong acid to lower the \(\text{pH}\) from \(7.0\) to \(2.0\). Which of the following correctly ranks the salts from greatest to least increase in molar solubility upon acidification, and provides the correct justification?
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